Controlled Atmosphere Storage of Grain

Abstract

Controlled atmospheres (CA) are used as periodic treatments to control pests (insects and mites) in stored grain or, less frequently, as long-term storage environments to prevent pest occurrence (insects, mites, and molds) or spontaneous combustion, as in poppy seeds that must be stored in nitrogen gas (Mills, 1989). The CAs contain either high levels of carbon dioxide (CO2), or high levels of nitrogen (N2), with virtual elimination of oxygen (O2). Grain in bulk storage is an immature ecosystem (Sinha, 1995) consisting of the living grain itself, numerous species of insects, mites, and molds, both on and in the seed. The nonliving part of the system includes humidity and grain moisture, temperature, and intergranular gases. When the grain is warm ( 25° C) or becomes moist, owing to bin leakage or to moisture migration by convection currents, the biological organisms begin to respire. Oxygen is consumed and heat, moisture, and carbon dioxide are produced. Canada has a legally defined zero-tolerance for insect pests in stored grain; hence, they must be controlled whenever detected. Dozens of insects are found in stored grain (Sinha and Watters, 1985) in low numbers, and many are fungus feeders that do not directly feed on the grain (White et al., 1995a). The most common grain-feeding insects in western Canada are the rusty grain beetle, Cryptolestes ferrugineus (Stephens) and the red flour beetle, Tribolium castaneum (Herbst), often being detected in up to 46% of farm granaries (Madrid et al., 1990). The whole-seed feeders—the rice weevil Sitophilus oryzae